2nd World Conference on Biomass for Energy, Industry and Climate Protection, 10-14 May 2004, Rome, Italy
COMPARISON OF SWITCHGRASS (Panicum virgatum L.) GENOTYPES AS POTENTIAL ENERGY CROP M. Grigatti, L. Barbanti, G. Pritoni, G. Venturi Department of Agroenvironmental Science and Technology - University of Bologna Viale Fanin 44, 40127 Bologna – Italy Fax: +39 051 2096241. E-mail:
[email protected] ABSTRACT: Seven genotypes of Panicum virgatum L., a perennial grass crop, were compared over two growing seasons in order to investigate potential biomass yield, its stability in time, and to assess nitrogen and ash content as characteristics detrimental to utilization in the energy chain. Crops were planted in May 2002, harvested in February 2003 for the first year; in February 2004 and in July 2003 + February 2004 for the second one. The two early, upland octaploid genotypes (Shawnee and Trailblazer) performed a lower yield associated to a lower moisture and to a higher ash content. The remaining five lowland tetraploids featured variable traits: NL 94-1, SL 93-3 and SL 94-1 had the best performances in terms of biomass yield and ash content; Alamo and Kanlow had an intermediate behaviour between them and the two octaploids. In the second year, the double harvest (summer + winter) showed a 50% yield increase with respect to the single one, associated to an undesirable peak in nitrogen and ash impurities. Keywords: Switchgrass, Biomass production, Ash. 1
INTRODUCTION
Perennial, herbaceous energy crops offer a great opportunity to improve agricultural sustainability in terms of crop diversification, improved control of soil erosion and recovery of soil organic matter content. Furthermore, reduced crop input reflects positively on soil and water environmental quality [1], as well as on the landscape. Its perennial habitus is an added value for cultivation in marginal lands, sloping and/or prone to soil erosion. Switchgrass is a warm season C4 grass, native of Midwestern and South-Eastern US, with a good potential of yield in many European Countries such as Italy. A suitable utilization as a biofuel requires low ash and nitrogen contents and, conversely, high lignin and cellulose [2]. Across the native regions, switchgrass has evolved into two types: lowland ecotypes (vigorous, tall, thick-stemmed, well adapted to wet condition) and upland ones (short, rhizomatous, thin-stemmed, well adapted to dry conditions). Switchgrass can be used for the production of energy through direct combustion, or combustion of fermentation products such as ethanol [3]. 2
MATERIALS AND METHOD
Seven genotypes were included in the study; two upland octaploids (Shawnee, Trailblazer) and five lowland tetraploids (Alamo, Kanlow, NL 94-1, SL 93-3, SL 94-1). They were compared over two years in Ozzano (Bologna, Italy) in a hilly area. Since the second year, two harvest patterns were carried out: winter harvest and summer + winter one. The crop trial was planted on May 7, 2002. Experimental plots were established in a randomized complete block design (four replications) with a split-plot arrangement: plot for genotype, sub-plot for harvest; the latter was 16,5 m² of surface. Harvest dates were Feb. 13, 2003, Jul. 3, 2003 and Feb. 10, 2004. Machine cutting followed by manual harvesting and weighing was done on a surface of 6,6 m2. 2.1 Ash and nitrogen determination Samples from the harvested plots were submitted to ash determination on 3 g of ground sample by furnace combustion at 550 °C until constant weight, and to the
analysis of total kjeldahl nitrogen (TKN) on 1 g of ground sample. Results are expressed on a dry basis. 2.2 Statistical analysis ANOVA was performed on two separate data sets: the first one was composed of the winter harvests in the two years; the second one, of the two harvest patterns in the second year. Significant differences were expressed as Fisher’s Lowest Significant Differences at p = 0,05 (LSD0.05). 3
RESULTS AND DISCUSSION
3.1 Winter harvests Biomass yield averaged 18 t ha-1 over the two years. Wide variations were observed between genotypes: the two upland octaploids always yielded less than the five lowland tetraploids (table I). The year factor significantly affected yields, too: 2002 had a favourable, cool and wet summer, while 2003 a very hot and dry one. It is perceived as this occurrence may have curbed yield potential in the second year, after crop establishment had been accomplished in the first one. The year effect did not reflect on dry weight, thanks to the higher dry matter content of the second year. The two early octaploids, Shawnee and Trailblazer, featured the lowest yields, below 9 t ha-1, associated to a dry matter percent of about 80%. The rest of the genotypes yielded above 11 t ha-1, with SL 93-3 and SL 94-1 as the top performers. Their relative lateness is shown by the lower percent of dry matter at maturity, in the range of 60 ÷ 70%. Achieving a good yield with a low moisture is a key goal in plant breeding for biofuels, since it allows the best possible yield with the lowest constraints in terms of transport and/or conditioning costs before actual utilization. In this respect, NL 94-1 showed the best compromise, thanks to a yield in the same range as the top performers (SL 93-3 and SL 94-1), and to an intermediate level of dry matter. A significant interaction was also observed concerning dry matter, between years and genotypes (fig. 1): in the dry year (2003), also late types such as Alamo, SL 93-3 and SL 94-1 attained a good maturity in terms of dry matter, while in the wet one (2002), they remained quite moister until harvest. Conversely, NL 94-1 was the least affected by weather variations between the two years. 261
2nd World Conference on Biomass for Energy, Industry and Climate Protection, 10-14 May 2004, Rome, Italy
Both TKN and ash impurities showed differences according to genotypes and to years: as for years, it cannot be stated whether the decreases observed in the second one are due to the higher thermal sum and to the subsequent better maturation of the plants, or to the completed establishment of the perennial crop, enabling a better translocation of nutrients to storage roots. Table I: Biomass (FW), dry matter yield (DW), dry matter content (DM), total kjeldahl nitrogen (TKN) and ash content in Switchgrass genotypes in two years. Genotype
Harvest
Alamo Kanlow NL94-1 Shawnee SL93-3 SL94-1 Trailblazer LSD 0.05 Feb.-03 Feb.-04
Genotype x Harvest
FW (t ha-1) 20,3 17,9 19,3 9,4 23,6 25,1 10,9 *** 4.14
DW (t ha-1) 11,7 11,8 13,2 7,3 13,9 14,4 8,7 *** 2.28
DM (%) 59,7 66,9 69,7 77,1 61,1 60,4 80,1 *** 5.30
TKN (mg g-1) 8,9 6,6 6,6 7,5 8,0 7,9 6,4 ** 1.41
Ash (%) 5,3 4,5 4,4 5,7 4,7 4,6 6,1 ** 0.98
19,7 16,4 *
10,9 12,2 n. s.
60,2 75,5 ***
9,5 5,3 ***
6,3 3,8 ***
**
n.s.
***
n.s.
n.s.
*P
